1. Field of the Invention
The invention relates to a locking device for a safety belt retractor comprising a reel shaft and a ratchet wheel that can be brought into engagement with pawls.
2. Description of the Prior Art
Many such retractors are known wherein a rotary motion is converted into an axial motion. For example, U.S. Pat. No. 3,970,265 describes one such retractor wherein a ratchet wheel, which is rigidly connected to the wheel shaft cannot be engaged directly with pawls secured to the housing but wherein an inertial wheel, rotatably disposed on the reel shaft and axially displaceable, is engageable with pawls by means of teeth disposed on the side of the inertial wheel opposite to the pawls. The ratchet wheel is provided with ratchet-type teeth or engagement bevels, and the inertial wheel which normally engages the ratchet wheel is provided with corresponding bevel-shaped recesses. The beveled surfaces of the ratchet wheel and of the inertial wheel which face each other permit a slipping movement to take place when the last-cited wheels rotate relative to each other, resulting in an axial movement of the inertial wheel onto the pawls. This, finally, causes effective engagement between the pawls and the engagement teeth on the inertial wheel which stops the inertial wheel and this, in turn, through the ratchet wheel, blocks the entire reel shaft.
When, in the use of this known belt retractor, during an accident, the belt is suddenly withdrawn at high acceleration, the ratchet wheel will follow this accelerated rotation, but the inertial wheel, because of its large inertial mass, will lag behind resulting in rotation of the ratchet wheel relative to the inertial wheel and the aforedescribed blocking of the reel shaft.
Many motor vehicle manufacturers insist on close locking tolerances, i.e., the belt retractor must be able to block within a narrow and exactly defined acceleration range. The aforedescribed, known belt retractor does not meet such tolerance requirements unless the spring is modified, and particularly not in cases where the shaft is disposed vertically and not approximately horizontally. Moreover, the mutually engaging teeth and pawls frequently are not ideally sharp so that frequently the tips of the teeth and pawls just touch each other and as a result valuable time is lost while the reel shaft continues to turn and the belt is further withdrawn from the retractor, until the slipping tooth tips finally engage the corresponding tooth system and bring about blocking. Moreover, the known belt retractor responds adversly to axial impact in the direction of the axial blocking motion of the inertial wheel. The inertial mass of said inertial wheel, namely, in reacting to the impact tends to move away from the pawls while the engagement bevels ensure that the teeth engage the pawls. This, too, will extend the unsafe time interval between the condition just before the engagement of the corresponding tooth systems and effective and complete engagement.
Another known belt retractor, described in U.S. Pat. No. 3,802,642, has similar drawbacks and also requires adjustment during installation. On axial impact of the motor vehicle, here, too, the inertial wheel is disengaged by the bevels of the ratchet wheel and pressed into the unlocked position in the direction opposite to that of disengagement. As a result, the desired locking cannot occur with the required precision and within narrow locking tolerances. This situation remains unchanged even when a "pocket" having an annular internal surface is used which swings out in the event of sudden deceleration of the motor vehicle and by touching an edge of the inertial wheel also causes said wheel to slow down.
The belt retractor according to U.S. Pat. No. 3,929,300 although not responding to axial impact of the aforedescribed type is not provided with axially displaceable inertial wheels. The cited patent describes two ratchet wheels which on their circumferential surface are provided with teeth. When in an accident the belt is suddenly rapidly withdrawn at high acceleration, these wheels simply move through a rotation angle into engagement with a toothed locking ring, said wheels then absorbing the entire locking force. The wheels can only rotate relative to the reel shaft but are not axially displaceable.
According to an older proposal, finally, a belt retractor is provided with a ratchet wheel, a pawl and a complicated pawl-actuating device with which, both in the event of motor vehicle acceleration and on rapid belt withdrawal, an actuating arm brings the pawl into engagement with the ratchet wheel. The vehicle-sensitive actuating device is equipped with a weak gear and a thin pawl. If, in an accident, while engaging the ratchet wheel, this pawl does not find a tooth space, it is protected from damage by a coupling disk which acts as a slip clutch and prevents the narrow, thin pawl or the weak actuating gear from breaking.